1. Field of the Invention
The invention relates to an extrusion die for making a hollow-chamber profiled panel of thermoplastic plastic with an interior coextruded layer.
2. Discussion of the Background
German Patent DE 2544245 describes the use of panes of polymethyl methacrylate with a content of light-reflecting particles aligned parallel to the surface. The pigment particles used for this purpose impart, in the infrared region, selective reflection having a selectivity coefficient of greater than 1. TiO2, lead carbonate and bismuth oxychloride are named as IR-reflecting pigments. The use of TiO2 pigment of the anatase type, deposited in a layer thickness of about 120 xcexcm on mica lamellas, is emphasized as particularly advantageous.
The particles are dispersed in concentrations of 0.01 to 1 wt % in a partly polymerized methyl methacrylate. The suspension is then fully polymerized to polymethyl methacrylate in a chamber between two glass plates. If this chamber is oriented horizontally, the pigment/mica particles contained therein become strongly aligned parallel to the pane surface as they settle, and so the desired IR-reflecting effect is developed in the fully polymerized panes. This parallel alignment of the IR-reflecting particles can be further improved by additionally rotating the glass plates of the chamber relative to one another a few times while the polymerizing material is still in the gel state.
DE 2544245 further mentions the possibility that the IR-reflecting pigments can also be incorporated in molding compounds. In such cases the pigments are supposedly aligned largely parallel to the surface during processing by calendering, extrusion or injection molding.
European Patent EP A 0548822 describes transparent, IR-reflecting members with sun-blocking and thermally insulating effect, such as plates, web plates or domelights, having a transmission (T) in the visible region of 45 to 75%, a total spectral transmission (g) of 30 to 60% and a T/g ratio of  greater than 1.15 (per DIN 67507). These IR-reflecting members can be made by coextrusion or coating processes such as lacquering or by reverse-roll coating from a stiff, amorphous base material of transparent plastic and a transparent coating material having a content of 20 to 40 wt % of red-reflecting and IR-reflecting particles comprising titanium dioxide deposited in a layer of 60 to 120 nm thickness on a lamellar substrate pigment. These IR-reflecting particles are contained in a coating layer of 5 to 40 microns thickness, adhering to the base material and comprising a transparent, water-insoluble binder, and are aligned parallel to the surface. In the examples, TiO2 pigments of the rutile type are used. For coextrusion it is recommended that the binder selected for the IR-reflecting layer have lower melt viscosity than that of the base material.
Examples of commercial products are multiple-web plates of polymethyl methacrylate with coextruded IR-reflecting finish according to EP A 0548822. Also known are multiple-web plates of polycarbonate with appropriate IR-reflecting finish, wherein a further coextruded layer containing UV absorbers is also disposed on the coextruded pigment layer to impart weathering resistance.
DE 19618569 A1 describes a multi-layer interference pigment comprising a transparent substrate material coated with alternating layers of metal oxides having low and high refractive indices, the difference in refractive index being at least 0.1. In this way mica lamellas, for example, can be provided with an alternating layer of TiO2SiO2/TiO2. Pigments such as described in DE 19618569 A1 are suitable for pigmenting sheetings for agricultural purposes, in order to hold back the infrared radiation of the sun and thus to prevent excessive heating, for example of greenhouses.
EP A 0733754 describes multiple-web plates made of impact-modified polymethyl methacrylate. It is further mentioned that it is possible to provide the inventive multiple-web plates additionally on the exterior or interior side with functional layers, such as scratch-resistant, anti-reflecting, water-repellent or even IR-reflecting coatings.
EP 0657280 describes a method for making plates of polycarbonate with a plurality of coextruded layers, which can contain pearlescent pigments and/or UV absorbers.
EP 0774551 A1 describes web plates of plastic, especially polycarbonate, which can contain, for example, IR-reflecting metal oxide pigments and UV absorbers in thin coextruded layers.
DE 19729093 C2 describes a method and a die for making web plates with a coating applied in the manner of stripes by coextrusion, for example with a coextrusion compound containing IR-reflecting pigments. It is mentioned that the coating can be applied both on the exterior and on the interior side of the chamber. However, the illustrated die is suitable only for exterior coating. In this method the coextrusion layer is applied in stripes on the base molding compound via a plurality of ducts in the outlet region of the profiling nozzle. It remains an open question as to how a corresponding interior coating would be achieved.
Thus, it is an object of the present invention to provide a die with which hollow-chamber profiled panels of thermoplastic plastic with a layered structure can be made from a top and bottom layer of one plastic melt and a layer of another plastic melt disposed in the interior of the hollow-chamber profile. Since only two plastic melts are needed, it is another object to avoid using more than two extruders for this purpose, in order to keep handling in the extrusion process simple and to minimize otherwise unavoidable startup, regulation and proportioning problems.
This and other objects have been achieved by the present invention the first embodiment which includes an extrusion die, comprising:
a distributing tool;
a profiling nozzle; and
at least three melt-flow ducts;
wherein a first melt-flow duct is routed around a second melt-flow duct or the distributing tool using a branch and is merged again downstream from the branch;
wherein a third melt-flow duct opens into the second melt-flow duct;
wherein said extrusion die is suitable for extrusion of a hollow-chamber profiled panel of a thermoplastic plastic with a layered structure;
wherein said layered structure comprises a top layer and a bottom layer of a first plastic melt; and an intermediate layer of a second plastic melt disposed in an interior of a hollow chamber profile;
wherein said first plastic melt is allocated to said first melt-flow duct and to said second melt-flow duct and the second plastic melt is allocated to said third melt-flow duct;
wherein during said extrusion said second plastic melt is deposited onto said first plastic melt upstream from or in the region of the branch, thereby obtaining a deposited second plastic melt;
wherein a distribution of the deposited second plastic melt is regulated using the distributing tool;
wherein said second melt-flow duct conveying the first plastic melt and the deposited second plastic melt is then merged with the first melt-flow duct in the profiling nozzle, whereupon the first plastic melt from the first melt-flow duct is deposited on the second plastic melt from the second melt flow duct, to sandwich the second plastic melt between two layers of the first plastic melt, thereby obtaining united plastic melts; and
wherein the united plastic melts are shaped to said hollow-chamber profiled panel during ejection from the profiling nozzle.
In another embodiment the present invention includes a process for making a hollow-chamber profiled panel, comprising:
coextruding a first plastic melt and a second plastic melt using the above extrusion die.
In yet another embodiment the present invention relates to a hollow-chamber profiled panel made by the above process.